1. Field of the Invention
The invention relates to a process for the production of aminomalonic acid dinitrile salts.
2. Background Art
It is well known to isolate aminomalodinitrile as p-toluenesulfonate by the reduction of oximinomalonic acid dinitrile with aluminum amalgam. But this production is protracted and complicated. Amalgamation of the aluminum causes difficulties, since the mercury layer does not adhere well to the surface of the aluminum. Moreover, much of the product remains in the precipitate when the aluminum hydroxide is suctioned off after the reduction [J. P. Ferris and L. E. Orgel, J. Am. Chem. Soc. 87, 4976-7 (1965); J. P. Ferris and L. E. Orgel, J. Am. Chem. Soc. 88, 3829-31 (1966); J. P. Ferris, U.S. Pat. No. 3,670,007 (1972), C.A. 77, 100866v (1972); J. P. Ferris, R. A. Sanchez and R. W. Mancuso, Org. Synth. 48, 1-3]. In U.S. Pat. No. 3,670,007, J. P. Ferris also describes reductions with zinc and sodium dithionite, but limits himself to the qualitative proof of aminomalonic acid dinitrile in the reaction solution.
A process is also known, in which oximinomalonic acid dinitrile is reacted in the presence of Raney catalysts as the reduction agent at hydrogen pressures of 5 to 7 bars (4 to 6 ata) and temperatures of 10.degree. to 80.degree. C. in tetrahydrofuran as the solvent. The aminomalonic acid dinitrile is precipitated from the reaction solution by treatment with p-toluenesulfonic acid and is isolated as tosylate or reacted in acetic anhydride as the solvent to aminomalonic acid dinitrile. The latter is precipitated and is isolated as acetyl aminomalonic acid dinitrile (European Published patent application No. 3353). According to such process yields of 27 to 49 percent are obtained.